[PATCH v2 2/2] ext4: protect ext4_release_dquot against freezing

[Ojaswin Mujoo <ojaswin@linux.ibm.com>]

Protect ext4_release_dquot against freezing so that we
don't try to start a transaction when FS is frozen, leading
to warnings.

Further, avoid taking the freeze protection if a transaction
is already running so that we don't need end up in a deadlock
as described in

  46e294efc355 ext4: fix deadlock with fs freezing and EA inodes

Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
---
 fs/ext4/super.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 16a4ce704460..f7437a592359 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -6887,12 +6887,25 @@ static int ext4_release_dquot(struct dquot *dquot)
 {
 	int ret, err;
 	handle_t *handle;
+	bool freeze_protected = false;
+
+	/*
+	 * Trying to sb_start_intwrite() in a running transaction
+	 * can result in a deadlock. Further, running transactions
+	 * are already protected from freezing.
+	 */
+	if (!ext4_journal_current_handle()) {
+		sb_start_intwrite(dquot->dq_sb);
+		freeze_protected = true;
+	}
 
 	handle = ext4_journal_start(dquot_to_inode(dquot), EXT4_HT_QUOTA,
 				    EXT4_QUOTA_DEL_BLOCKS(dquot->dq_sb));
 	if (IS_ERR(handle)) {
 		/* Release dquot anyway to avoid endless cycle in dqput() */
 		dquot_release(dquot);
+		if (freeze_protected)
+			sb_end_intwrite(dquot->dq_sb);
 		return PTR_ERR(handle);
 	}
 	ret = dquot_release(dquot);
@@ -6903,6 +6916,10 @@ static int ext4_release_dquot(struct dquot *dquot)
 	err = ext4_journal_stop(handle);
 	if (!ret)
 		ret = err;
+
+	if (freeze_protected)
+		sb_end_intwrite(dquot->dq_sb);
+
 	return ret;
 }
 
-- 
2.43.5